1. Field of the Invention
A transflective electrophoretic display device is disclosed, and more particularly, a device employing a plurality of color particles affected by an electric field is introduced to display monochrome or color images.
2. Description of Related Art
A electrophoretic display device, which comprises a plurality of charged particles controlled by a provided electric field, displays by changing reflectivity in a display region therein relative to a surrounding light. The display device has the following features: (1) it's flexible; (2) it incorporates the surrounding light to improve visibility; (3) it can be manufactured by roll-to-roll process, so it has a high yield and reduces the yielding cost; (4) since there is no limit to the viewing angle, the device can be seen from any point of view; (5) it's not sensitive to the distance variation between two panels; (6) the electrophoretic display device has bistability, which is one of the most important characteristic of a flexible display device.
The surface of particles can be charged by being ionized or absorbing other charged particles. When charged particles of an electrophoretic display device are activated by an external electric field, they will move to the opposite direction relative to the electrode with opposite charges. A plurality of factors such as particle type, particle diameter, particle concentration, and the intensity, distribution and direction of the external electric field, and the type of the display solvent of the particles mentioned above will cause different moving speeds of the particles and achieve different displaying purposes.
U.S. Pat. No. 6,750,844 discloses a pliable electrophoretic display device having a deformation-resistant memory characteristic provided by covering a plurality of partitioning walls defining display sections containing a dispersion liquid with electrophoretic particles dispersed therein with an expandable ceiling sheet. U.S. Pat. No. 6,751,007 and No. 6,750,844 further disclose that the partitioning walls with high strength are disposed between the display cells. Wherein, the shape, size and the aspect ratio of the partitioning walls cause the embodiment of the display device. The plurality of pigment particles are dispersed in the solvent, and microcup technology is introduced in these prior arts. The mentioned display device with microcup structure can ignore the boundary sealing of each display cell, and accomplishes a flexible feature.
U.S. Pat. No. 6,751,007 provides a transflective electrophoretic display of SiPix Imaging, Inc. Reference is made to FIG. 1A, which shows one of a plurality of display cells 103 divided by the partitioning walls 109, and forms a display device. The cell 103 includes a top substrate 101, a bottom substrate 102 with electrodes, surrounding partitioning walls, and a plurality of pigment particles 104 in the display solvent 105 filled in a space isolated by the plurality of partitioning walls 109, and the display cell 103 is sealed by a sealing layer 106, and finally a backlight module 107 is disposed to compensate for the displaying of the electrophoretic display device.
An electric field is generated by the electrodes in the top or bottom substrate as shown in FIG. 1A, and an electric field is used to affect the behavior of the pigment particles 104 in the display solvent 105. The types of the electric field include an up/down switching mode, an in-plane switching mode and a dual switching mode. As shown in FIG. 1A, the top substrate 101 can be a conducting glass such as Indium Tin Oxide (ITO), and the bottom substrate 102 includes in-plane electrodes 110a and 110b divided by the partitioning slabs 112 and the bottom electrode 111.
Furthermore, U.S. Pat. No. 6,639,580 (Electrophoretic Display Device and Method for Addressing Display Device) discloses the technology of an in-plane electric field. Wherein the in-plane electrode generates an in-plane electric field to change the status of the charged particles in the display solvent and generate various display effects.
FIG. 1B shows a display device of the prior art formed by a plurality of display cells 103 including a plurality of microcups arranged in a rectangular array. The display cell 103 of one of the embodiments includes primary colors such as red, green and blue for displaying color, namely, a three-monochromatic display cell forms a chromatic display cell.
The chromatic display cell 20 shown in FIG. 2A includes three separated primary color sub-display cells. A plurality of white charged pigment particles 24 in the colorless display solvent 25 scatters the light emitted from the backlight module. Another embodiment shows the filtering plates 21, 22 and 23 with red, green and blue disposed in these sub-display cells.
An electric field with a different status generated by the electrodes disposed in the bottom substrate is used to guide the behavior of the charged pigment particles 24, and further results in the scattering effect mentioned above. The primary color filtering plates 21, 22 and 23 are used to display a variety of color effects. In yet another embodiment, a further displaying result occurs if the white pigment particles 24 are changed to light-absorbed black pigment particles.
FIG. 2B shows a chromatic display device of the prior art. The display cell 20 includes three sub-display cells with red, green and blue colors. The colorless and transparent display solvent 25 includes color pigment particles 26, 27 and 28, which are red pigment particles 26, green pigment particles 27 and blue pigment particles 28 respectively. The electric field is changed by the electrode in the bottom substrate with black or white plates. Those color pigment particles 26, 27 and 28 in the display solvent 25 are then activated to display various effects.
The reflective-type electrophoretic displayer of the prior art doesn't function when the surrounding light is weak or nonexistent. Moreover, the transmissive-type electrophoretic displayer is not adaptable to portable devices since it consumes a lot of power.
Some drawbacks are associated with the technology having partitioning walls in the prior art provided by the SiPix Imaging, Inc. Since the partitioning walls 109 are used as the medium for the backlight, this allows the electrophoretic displayer to operate in the dark, but the partitioning walls may possibly cause light leakage. Moreover, the backlight doesn't go through the display solvent directly, so it doesn't provide a quality of high display. Meanwhile, the electrophoretic displayer includes both the reflective-type and the transmissive-type, so it has complicated design and is difficult to fabricate.
In view of the aforementioned drawbacks of the prior art, the present invention provides a transflective electrophoretic display device, which facilitates illumination effects since both the surrounding light and the backlight can go through the display solvent completely. Meanwhile, the backlight module can be adjusted based on the condition of surrounding light, and effectively enhances the contrast of the display and reduces power consumption. Furthermore, the present invention has a simplified design and higher manufacturing yield.